960 Engine "Ping" With Varied Octanes

zippinbye · Post by **zippinbye** » 18 Jun 2013, 21:31

Our 1995 960 has been pinging under load. Not really noticeable under light to moderate acceleration, but it's significant while climbing a grade or with heavy throttle. I can't say if the engine is putting out full power, as I have always felt like it's underpowered since purchased last fall (my first Volvo). But I didn't expect impressive performance; it's generally smooth and as expected for humble power in a heavy sedan. It's pulling about 19 mpg in mixed driving, which I think is decent for a 960. I'm pretty sure the problem is classic predetonation. I've experimented with octanes between 87 and 91. While there's a difference, it's not dramatic. 91 did not eliminate the ping, and an octane booster added in a quantity to attain 100+ did not make the ping go away entirely. While I'm guilty of being a Volvo newbie who has yet to obtain a service manual, I'm pretty sure the 2.9L engine has computer controlled ignition timing with no provision for adjustment. So I am guessing that there's an anti-knock sensor or other system component that's not doing its job. Any ideas on where to start to figure this out?

Post by **jimmy57** » 18 Jun 2013, 21:46

Knock sensor failure readily sets codes so I would not be suspect of that. Also 91 octane should make the knock sensor function irrelevant as it would ping on 91 without some other fault.
Timing belt marks need to be veririfed.
It is possible to have a faulty oxygen sensor and run lean and ping.
Full scan tool can read fuel trims to see that fuel trims are in range. Usually if they are off enough to ping you would have check engine light. Your check engine light does illuminate when key is on before engine is started?

zippinbye · Post by **zippinbye** » 22 Jun 2013, 18:15

jimmy57 wrote: Your check engine light does illuminate when key is on before engine is started?

I just noticed the the CEL is not illuminating on start-up. Nor is SRS. All other dash annunciators test okay on start-up, although I am having an intermittent background lighting problem (separate topic that I just started).

Any ideas?

Post by **jimmy57** » 22 Jun 2013, 21:10

Then it may have codes that will point to the problem. If the check engine light bulb is burned out then you wouldn't have an obvious indication of codes present.